This invention relates to devices which detect and/or treat tachyarrhythmias (rapid heart rhythms), and more specifically, to mechanisms to distinguish among various tachyarrhythmias and to provide appropriate therapies to treat the identified tachyarrhythmias.
Early automatic tachyarrhythmia detection systems for automatic cardioverter/ defibrillators relied upon the presence or absence of electrical and mechanical heart activity (such as intra-myocardial pressure, blood pressure, impedance, stroke volume or heart movement) and/or the rate of the electrocardiogram to detect hemodynamically compromising ventricular tachycardia or fibrillation. Presently available pacemaker/cardioverter/defibrillator arrhythmia control devices, such as the Model 7219 and Model 7221 implantable pacemaker/cardioverters/defibrillators commercially available from Medtronic, Inc., employ programmable fibrillation interval ranges and tachycardia detection interval ranges, along with measurement of suddenness of onset and rate variability.
For future generations of devices, numerous detection and classification systems have been proposed. Numerous patents, including U.S. Pat. No. 5,217,021 issued to Steinhaus et al., U.S. Pat. No. 5,086,772 issued to Lanard et al., U.S. Pat. No. 5,058,599 issued to Andersen and U.S. Pat. No. 5,312,441 issued to Mader et al propose waveform morphology analysis systems for determining the type and origin of detected arrhythmias. Other patents, including U.S. Pat. No. 5,205,583 issued to Olson, U.S. Pat. No. 5,913,550 issued to Duffin, U.S. Pat. No. 5,193,535 issued to Bardy et al., U.S. Pat. No. 5,161,527 issued to Nappholz et al., U.S. Pat. No. 5,107,850 issued to Olive and U.S. Pat. No. 5,048,521, issued to Pless et al. propose systems for analysis of order and timing of atrial and ventricular events. Complex dual chamber detection mechanisms which rely upon a sets of ordered rules which are applied to distinguish between various atrial and ventricular arrhythmias are disclosed in U.S. Pat. No. 5,545,186, issued to Olson et al. and in pending U.S. application Ser. No. 08/895,342, filed on Jul. 17, 1997 by Gillberg et al. for a "Prioritized Rule Based Method and Apparatus for Diagnosis and Treatment of Arrhythmias .
In spite of the extensive work done toward optimizing detection methodologies, there are still situations in which improvements in detection methodology are to be desired. One such situation is the detection and classification of rhythms which may be due to atrial fibrillation and/or atrial flutter. In some cases, these two rhythms are difficult to distinguish, and in other cases, the patient may move between the two types of rhythm, during either the detection process or during the process of delivering an electrical therapy to terminate the rhythm.